This invention relates to aqueous emulsion copolymers comprising from about 2% to about 20% of ethylene, from about 20% to about 78% of vinyl acetate, and from about 20% to about 60% of a functionalized monomer selected from the group consisting of acid containing monomers, nitrogen containing monoolefinically unsaturated monomers, and hydroxyl containing monomers. The present invention also pertains to methods for making the ethylene vinyl acetate aqueous emulsion copolymers containing high concentrations of functionalized monomers and to ethylene vinyl acetate aqueous emulsion copolymers made by the novel methods.
The preparation of ethylene vinyl acetate (EVA) polymers using emulsion polymerization techniques with medium pressure equipment is known. Incorporation of more than 5% (wt/wt) of a functionalized comonomer is difficult in emulsion polymerization because of many factors. First, it is important to cntrol the pH of the emulsion because functionalized monomer reactivity and emulsion stability vary with pH. Second, polymerization of functionalized monomers in the aqueous phase can lead to high viscosity emulsions and grit formation. Third, differences in monomer reactivity ratios often result in non-homogeneous copolymers. Fourth, levels of acrylic acid higher than 1.5% (wt/wt) inhibit the batch copolymerization reaction of ethylene and vinyl acetate. Fifth, incorporation of large amounts of functionalized monomer in the growing polymer creates a polar micellar environment that discourages migration of gaseous ethylene to the micelles.
Various methods have been employed to incorporate large amounts of functionalized monomers into ethylene vinyl acetate copolymers. For example, U.S. Pat. No. 5,171,777 (Kuphal et al.) describes physical blends of ethylene vinyl acetate copolymers and polymers of acrylic acid. The use of polyvinyl alcohol (PvOH ) stabilization systems is described in EP 389,893 (Lenney) which claims 2-6% (wt/wt) acrylic acid incorporation although the examples only disclose 4% acrylic acid. U.S. Pat. No. 5,120,785 (Walker et al.) discloses the use of acrylic monomers to overcome the reactivity ratio problem of acrylic acid and claims up to 5% (wt/wt) acrylic acid. U.S. Pat. Nos. 5,109,063 (Cheng et al.), 4,698,384 (Mao), 4,449,978 (lacoviello""978), and 4,332,850 (lacoviello""850) disclose the use of N-methylol acrylamide (NMA) as a functional comonomer. The use of water-insoluble comonomers with acrylic acid and incorporation of 0.5-7% (wt/wt) acrylic acid is disclosed in U.S. Pat. No. 4,446,274 (Okazaki et al.). British patent GB 2,271,717 A1 discloses the grafting of acrylic or methacrylic acids onto ethylene vinyl acetate copolymers for medical or veterinary use. German patent DE 300,977 A7 teaches grafting of unsaturated monocarboxylic acids, such as acrylic acid, dicarboxylic acids, and anhydrides, such as maleic anhydride, using peroxide or a diazo containing initiator for use in coatings or impact modifiers. U.S. Pat. No. 5,591,799 (Bott et al.) discloses a stable aqueous emulsion containing water-insoluble, vinyl polymer particles formed by the emulsion polymerization of at least two ethylenically unsaturated monomers. The vinyl polymer comprises from 1% to 20% by weight of polymerized N-vinylformamide units and the polymerized N-vinylformamide units is hydrolyzed in a molar amount of from 8% to 30%.
None of the above disclosures describe a method for making ethylene vinyl acetate aqueous emulsion copolymers containing high concentrations of functionalized monomers. The present invention discloses methods for incorporating high levels of functionalized monomers into ethylene vinyl acetate aqueous emulsion copolymers and also discloses a novel class of self-reactive ethylene vinyl acetates having applications in the adhesive and coating formulation areas.
The present invention is directed to an aqueous emulsion copolymer comprising in percentages by weight of the total composition:
(a) from about 2% to about 20% of ethylene;
(b) from about 20% to about 78% of vinyl acetate; and
(c) from about 20% to about 60% of a functionalized monomer selected from the group consisting of acid containing monomers, nitrogen containing monoolefinically unsaturated monomers, hydroxyl containing monomers, and mixtures thereof.
The present invention is also directed to a method for preparing an aqueous emulsion copolymer comprising the steps of:
(A) providing the following monomers in percentages by weight of the total composition:
(a) from about 2% to about 20% of ethylene;
(b) from about 20% to about 78% of vinyl acetate; and
(c) from about 20% to about 60% of a functionalized monomer selected from the group consisting of acid containing monomers, nitrogen containing monoolefinically unsaturated monomers, hydroxyl containing monomers, and mixtures thereof; and
(B) emulsion polymerizing the ethylene, vinyl acetate, and functionalized monomer in water at a solids level from about 35% to about 70%.
The present invention is further directed to a method for preparing an aqueous emulsion copolymer prepared by a method comprising the steps of:
(A) providing the following monomers in percentages by weight of the total composition:
(a) from about 2% to about 20% of ethylene;
(b) from about 20% to about 78% of vinyl acetate; and
(c) from about 20% to about 60% of a functionalized monomer selected from the group consisting of acid containing monomers, nitrogen containing monoolefinically unsaturated monomers, hydroxyl containing monomers, and mixtures thereof; and
(B) emulsion polymerizing the ethylene, vinyl acetate, and functionalized monomer in water at a solids level from about 35% to about 70%.